The present application relates to a separator and a battery using the separator and, more particularly, to a separator for insulating a cathode and an anode and a battery using the separator.
Owing to the remarkable development of the recent portable electronic techniques, cellular phones and notebook-sized computers have been recognized as fundamental techniques which support an advanced information society. Studies and development to realize advanced functions of those apparatuses have vigorously been being progressed. There is such a problem that a driving time is shortened by an increase in electric power consumption due to the realization of the advanced functions.
To keep the driving time of a predetermined standard time or longer, since it is an indispensable condition to realize a high energy density of a secondary battery which is used as a driving power source, for example, a lithium ion secondary battery is expected.
In the examination to realize a high capacity and a high safety of the lithium ion secondary battery, in the case of only a polyolefin microporous membrane in the related art, since it is difficult to obtain enough performance, it is necessary to apply a function to the polyolefin microporous membrane. As a method of applying the function to the polyolefin microporous membrane, for example, a method whereby the polyolefin microporous membrane is coated with a resin having difference properties or the like has been proposed.
For example, in Patent document 1 (JP-A-2002-355938), there has been disclosed such a technique that a composite film which is obtained by forming a coating layer made of a porous substance B of a heat resistant polymer onto at least one surface of a polyolefin microporous membrane A and is characterized in that a mean hole diameter of the porous substance B is larger than the maximum hole diameter of the polyolefin microporous membrane A is used as a separator for a battery such as a lithium secondary battery. According to the separator disclosed in Patent document 1, by using a Scanning Electron Microscope SEM, it is confirmed that the coating layer formed on the obtained composite film has a porous structure and the hole diameters are measured. The confirmation and measurement are performed by an observation only from an upper portion of the coating layer.